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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Topic: V Twin
    Posted: 27 Jan 11 at 3:55pm
Originally posted by Phil eltringham

I have a number of questions, mostly to try and understand what you expect the waveform it will generate to be like as I can see it having a number of strange effects on the performance of the boat.  please indulge me...
 
Have you got as far as trying to model (numerically if not in CFD) the eddy, spray, added mass, and wave drag that will appear as the tunnel opens up under the hull? 

We've only modelled it in the CAD programmes and some sort of theoretical lift drag coefficient print out thing I don't fully understand, so no, dont yet know.


Originally posted by Phil eltringham

Have you also considered that as you move forwards the air presure in the tunnel will drop and suck the hull lower into the water? 

Hmm don't think so, too leaky, big cb slot for a start, and rocker is such that the nose of the tunnel should clear the surface.

Originally posted by Phil eltringham

What about if you are sitting back and you close the gap at the transom so there is now a sealed air pocket under the hull which you will be pulling along with you (as it is sealed it becomes part of the system and so is an added mass and hence drag).  

No, too much tail volume, you'd have to weigh 150 kilos and squat right on the stern and even then...

Originally posted by Phil eltringham


What if the wave coming off the split in the hull touches the bottom of the cross deck and seals the tunnel? 

Yes, this is one imponderable that's only going to get solved in the doing, as more worryingly is the potential vortex and turbulence ahead of the plate during that point when the tunnel entry water release is active.

Originally posted by Phil eltringham

As the hull is a scow bow there will be more buttock flow than waterline flow around the hull, especially compared with a fine bow and as a result squat will be a problem, personally i think that the tunnel will only add to this problem, and the reduced size of the planing surface means that the area available to generate dynamic lift is reduced and i can see getting over the hull speed 'hump' being something of a problem.   
Is the plan to sail it flat or flying a hull?

The plan is to do a bit of both.

But I take all your points and they are valid, hence a 'panic attack' the other day.

But as Dan said to me, my options to get a boat of these dimensions round a course in any normal design in anything other than light conditions is strictly limited by my height & weight and if this does the job more often than it doesn't, then I'm the winner by it.

It's got to be a compromise to do everything I'm expecting of it and for sure there are going to be things that aint right, but if it does mean I can get round a course in all weather half decently without pissing it in, pitch poling, death rolling and all the other fine things that these damn dinghies seem hell bent on doing to me, then I'll be happy and try to find ways round any of the issues that arise from this first attempt.

Then again I could think ooh too many problems I'll call it quits and not bother.

But then I'd never know which would be worse.
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Posts: 889 		Post Options Post Options   Quote laser193713 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 11 at 3:37pm
Just out of interest do you know the program being used to do the hullform design? The renderings seem a lot smoother than the ones I have done on maxsurf.  I cant help thinking this boat would be better backwards? with twin cat hull style bows and a large planing surface aft, the boat could still be sailed heeled upwind and the wetted area would then be low, and downwind sailed flat. 

Also what is your reasoning behind the clearly alto inspired swinging pole? on a single hander with eventually a trapeze you are going to have a lot on in the gybe!  If it does go as fast as it could potentially go downwind with that much rag then I dont think you are going to need to soak too much as the apparent wind should be moving forwards nice and early. 

What advantage does this have over the 100 which is possibly the easiest single handed assy around while still being lovely to sail and reasonably fast? The only possible issue of the 100 is the upwind speed, but thats only because it is so nice to sail off the wind that you just cant wait for the beat to end so you can get the kite up and have some real fun!

I would love to see this work, if it really takes off could we see the americas cup going back to (sort of) monohulls!? With GRF as chief designer for a GBR entrant!
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Posts: 628 		Post Options Post Options   Quote I luv Wight Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 11 at 3:36pm
Mr Aardvark tried a fully raking fwds backwards and sideways rig on a N12 a few years ago, but it was only a short time before it was converted to a 'normal' rig.
The rigs on the BOR tri and the Orma 60's are canting so the mast is vertical when flying on one ama.

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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 11 at 3:22pm
It's talk of the unwanted buttock flow that does it for me!
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Posts: 186 		Post Options Post Options   Quote simonrh Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 11 at 2:55pm


Originally posted by NickA

Like Rupert says:  

Doesn't that catapult cat have a side to side raking rig?  Ie sail it heeled with the mast upright?  You can let off the leeward shroud whilst sailing and pull in the windward one.  More string to play with!
 
Doesn't the catapult have adjustable shrounds to allow you to pull the hull half way up right when you have chucked it in before you start lifting the rig out of the water?
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Phil eltringham View Drop Down
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Posts: 1105 		Post Options Post Options   Quote Phil eltringham Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 11 at 2:16pm
I have a number of questions, mostly to try and understand what you expect the waveform it will generate to be like as I can see it having a number of strange effects on the performance of the boat.  please indulge me...
 
Have you got as far as trying to model (numerically if not in CFD) the eddy, spray, added mass, and wave drag that will appear as the tunnel opens up under the hull? 
Have you also considered that as you move forwards the air presure in the tunnel will drop and suck the hull lower into the water? 
What about if you are sitting back and you close the gap at the transom so there is now a sealed air pocket under the hull which you will be pulling along with you (as it is sealed it becomes part of the system and so is an added mass and hence drag).  
What if the wave coming off the split in the hull touches the bottom of the cross deck and seals the tunnel? 
As the hull is a scow bow there will be more buttock flow than waterline flow around the hull, especially compared with a fine bow and as a result squat will be a problem, personally i think that the tunnel will only add to this problem, and the reduced size of the planing surface means that the area available to generate dynamic lift is reduced and i can see getting over the hull speed 'hump' being something of a problem.   
Is the plan to sail it flat or flying a hull?
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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 27 Jan 11 at 1:26pm
Originally posted by Skiffman

does that triple stage rocker give better wakestyle pop
No not necessarily, if you want better 'wakestyle' pop you need one of the new Slingshot 'flex' wakeboards

Three stages of rocker alters the nose attitude according to boat(board) speed, something your 49er could do with.



Originally posted by NickA

Like Rupert says:  

Doesn't that catapult cat have a side to side raking rig?  Ie sail it heeled with the mast upright?  You can let off the leeward shroud whilst sailing and pull in the windward one.  More string to play with!

I had considered this, but it would need a serious amount of engineering and I'd figured I had enough going on trying to bring the rig back and forward and tbh thought moving the rig back would theoretically make more difference than canting it to windward.


Edited by G.R.F. - 27 Jan 11 at 1:27pm
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NickA View Drop Down
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Posts: 784 		Post Options Post Options   Quote NickA Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jan 11 at 8:39pm
Like Rupert says:  

Doesn't that catapult cat have a side to side raking rig?  Ie sail it heeled with the mast upright?  You can let off the leeward shroud whilst sailing and pull in the windward one.  More string to play with!
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Skiffman View Drop Down
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Posts: 291 		Post Options Post Options   Quote Skiffman Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jan 11 at 9:55am
does that triple stage rocker give better wakestyle pop
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Boydgt View Drop Down
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Posts: 31 		Post Options Post Options   Quote Boydgt Quote  Post ReplyReply Direct Link To This Post Posted: 25 Jan 11 at 12:01am
maybe of some interest
 


Edited by Boydgt - 25 Jan 11 at 12:06am
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